Managing unit for interrupt channels in a microcontroller

Abstract: A management unit (1) for microcontrollers equipped with a decoder (4) for a plurality (2N) of interrupt channels (2) is of a type connected to a central processing unit (11) of the microcontroller to decode and transfer thereto a single interrupt digital signal through said decoder (4), and comprises a first circuit portion (3) for selecting homolog pairs (A0,A1;B0,B1,...) of channels (2) incorporating a modular chain of elements (5,6), each having a respective channel pair (2) connected thereto (5,6). The first or selection portion (3) is associated with a second or decoding circuit portion (4), and the interrupt signal is a reform of the channel interrupt vector carrying higher priority in the channel pair selected by the chain.

Description: Field of the Invention This invention relates to an interrupt-channel management unit for microcontrollers. More particularly, but not solely, the invention relates to a management unit for microcontrollers which are provided with a decoder of interrupt channels, and the ensuing description will make reference to this field of application for simplicity of illustration. Background Art As is well known, in the pertinent art of this invention, electronic microcontrollers are available which include a management unit for interrupt signal channels. In general, each channel connects the management unit to a sensor, a transducer, or a peripheral circuit outside the microcontroller. Interrupt signals are digital signals which can be indentified by a vector having a number of bits equal to the number of the channels. Such signals are intended to trigger, according to necessity, the running of an interrupt procedure within the central processing unit of the microcontroller. This central unit will also be referred to briefly as the CPU hereinafter. Interrupt signals may carry different priorities; that is, one of them may be pre-eminent, or "win", over other requests for interrupts. Of course, a winning request would be served first. Usually, there are discrete circuit portions called "macro-cells" within the microcontroller which may receive as input a request for interrupt and can produce as output a similar signal to the CPU. For example, Figure 1 herein shows schematically the basic structure of a microcontroller 10 including a CPU 11, a counter 12, an interface 13, an A/D converter 14, and an interrupt channel management unit 15. The macro-cells 12, 13, 14 and 15 are all connected to the CPU to transfer a respective interrupt signal. Now, taking into consideration just the management unit 15 for the interrupt channels, it matters to observe that the CPU will "see" this unit 15 as a single macro-cell capable of generating a single interrupt signal carrying a given priority. However, in order for the unit 15 to effectively perform its function, it should in itself be capable of recognizing and selecting which request of interrupt carries the highest priority of the many which are directed to it on the various channels. Accordingly, the management unit must firstly perform a decoding to assess the winning channel from the many led to it, and then define the interrupt vector which is to be sent to the CPU. This usually involves the implementation of a complex decoding structure which occupies a large circuit area on the microcontroller. Such a decoding structure obviously must be commensurate to the number of the interrupt channels present in a given microcontroller. For example, four channels would require a decoder of a certain complexity, but double that number of channels would result in a decoding structure of extremely large bulk. The current trend favors microcontrollers which can accept an ever larger number of interrupt channels, and this poses the problem of how to accommodate the expanding size of the channel-managing unit. For example, with eight channels, a decoder with 2 8 =256 cells would have to be provided to just have eight viable vectors output. Up to now, interrupt channel management units with a wired logic have been provided, i.e. structures "tailored" to suit a specific microcontroller having a predetermined number of channels. Briefly, it has been impossible to match or transfer a management unit to other differently sized interrupt channels of another microcontroller without its internal structure and size having to be radically changed. EP489260 discloses an interrupt controller comprising an interrupt decoder section having a modular structure. This interrupt controller is easier to adapt but suffers from the drawback that the circuitry used in each module is relatively complex. The underlying technical problem of this invention is to provide an interrupt channel management unit which has structural and functional features whereby it can be used "adaptively", that is, readily adapted for use with other different sized microcontrollers whilst at the same time utilizing less complex circuitry than prior art rangement units. Summary of the Invention The idea on which this invention stands is that of providing an interrupt channel selector comprising a chain of modular elements which receive channel pairs to locate the "winning" pair, an interrupt vector being then located and reformed for the CPU within the winning pair. Based on this idea, the technical problem is solved by a unit as indicated above and defined in the characterizing clause of Claim 1. The features and advantages of a unit according to this invention will be apparent from the following detailed description of an embodiment thereof, given by way of example and not of limitation with reference to the accompanying drawings. Brief Description of the Drawings In the drawings: Figure 1 shows schematically a microcontroller incorporating an interrupt channel management unit; Figure 2 shows schematically a management unit, as incorporated to the microcontroller in Figure 1, which embodies this invention; and Figure 3 is a diagram illustrating the internal structure of the unit of Figure 2 in greater detail. Detailed Description With reference to the drawing Figures, generally and schematically shown at 1 is a management unit for interrupt signal channels 2 embodying this invention and being incorporated to an electronic microcontroller 10. The microcontroller comprises a central processing unit or CPU 11, and a plurality of macro-cells 12, 13, 14, all connected to one input of the CPU, designated INT. The first macro-cell 12 is a counter block, or TIMER; the second macro-cell 13 is a serial interface SCI; and the third macro-cell 14 is an A/D converter. The CPU handles directly a priority "arbitration" step among the interrupt signals which are supplied to it by the macro-cells. The channel 2 management unit 1 is also incorporated into a macro-cell which is "seen" by the CPU 11 as a "supplier" of an interrupt signal. In this case, the unit 1 has a digital output which is provided on an eight-bit data bus connected to the CPU 11 and designated DRB. It should be noted that the unit 1 may also be incorporated to the CPU 11, and hence, to a single integrated circuit. Alternatively, the unit 1 may be designed for implementation as a separate integrated circuit which can be connected and matched to microcontrollers having different interrupt channel management requirements. A plurality of channels 2 for interrupt signals are led to the management unit 1. In the embodiment being discussed herein by way of example, there are eight such channels 2, designated A0, A1, B0, B1, C0, C1, D0 and D1. However, the channels 2 may well be a smaller number, e.g. four, or a larger number, e.g. sixteen. On this account, the aggregate of the channels will be designated 2N hereinafter. Furthermore, it being convenient on occasions to analyze homolog channel pairs, i.e. even- and odd-numbered channels in one pair, reference will also be made hereinafter to N channel pairs rather than 2N channels. The management unit 1 for the N pairs of channels 2 comprises a first or selection circuit portion 3 and a second or decoding circuit portion 4. The first portion 3 includes a chain of elements 5 to which one of the N channel pairs is led. This chain provides a daisy chain wherein each element 5 is effective to activate, or deactivate, the element next to it. It should be noted, however, that the initial block in the chain, denoted by 6, has a peculiar structure which is distinguished from the other elements 5 connected after it. This feature makes the circuit portion 3 a hybrid daisy chain of sort, hereinafter referred to as "bonny chain". It is important to observe, moreover, that the number of the elements 5 in the chain could be equal to the number N of channel pairs. In actual practice, the number of the elements 5 in the chain would be N less two, because the initial block 6 cannot be taken to be identical with the other elements 5, and the last element 5 has been omitted since it can be isolated from the others by logic exclusion. The initial block 6 in the bonny chain comprises a CMOS inverter having a first or pull-up transistor M1 of the p-channel MOS type connected in series with a second or pull-down transistor M2 of the n-channel MOS type, which transistors are connected between a first supply voltage reference Vcc and a second voltage reference, such as a signal ground GND. The first transistor M1 has preferably a W/L (channel width/length) dimension of 10/1.5 µm, and the second transistor M2 has preferably a W/L dimension of 5/1.5 µm. The initial block must pre-charge the bonny chain as to initiate a sequential scanning of the signals present on the various pairs of interrupt channels. In this respect, the respective gate terminals of the transistors M1 and M2 are both connected to one input line which is applied a signal REQ-WA, which signal is re-initialized to ground by the microcontroller at the start of each instruction execution, that is before the "arbitration" step between macro-cells. This input line is also connected to the decoding circuit portion 4, to be described, specifically to an input of a storage element 17, such as a latch, through an enable transistor M7. The interconnection point between the transistors M1 and M2 is basically the output of the initial block 6, which output is connected to the input side of a first element 5 in the bonny chain. That first element 5 includes an incoming signal line B-CHAIN-A wherein a p-channel MOS transistor M4 is connected which has its drain terminal connected to ground via an n-channel transistor M5. The last-mentioned transistor receives a signal REQ-WB on its gate terminal which contains information about the interrupt priority of the second channel pair BO, B1. This signal is also applied to the gates of the transistor M4 and an n-channel transistor M3. The transistor M3 connects the input line B-CHAIN-A to the decoding portion 4 through the enable transistor M7. The drain terminal of the transistor M4 is further connected to ground via an n-channel transistor M6 which receives the input signal from the line B-CHAIN-A on its gate terminal via an inverter 8. The drain terminal of the transistor M4 also forms the output of the element 5, which output is connected to the input side of the next element 5 by a signal line B-CHAIN-B representing the input line for this next element 5. All the cascaded elements 5 have the same structure; but, to avoid burdening Figure 3 with too many references, only references for identical components, as incorporated to identical modular structures of both the circuit portion 3 and the circuit portion 4, have been shown in the Figure. As mentioned above, the last element 5 in the chain corresponding to the N-th channel pair has been omitted, and accordingly, the output of the element 5 in the N-1 position is connected directly to the decode portion 4 through the transistor M7 only. To now revert to the structure of the portion 4, it should be observed that to each element 5 or to the initial block 6 of the bonny chain there corresponds substantially an identical modular portion of the decoding circuitry. For example, all the transistors M7 associated with the input lines B-CHAIN are connected to a corresponding storage element 17. The output Q of the storage element 17 is transferred to the output through an inverter 16 to indicate the winning interrupt signal, e.g. VECT-A, for the initial block 6. The signal after the inverter 16 is also applied as input to the gate terminal of a transistor Mx in a complemetary pair incorporated to a bit selection cell 7. The cells 7 are connected in cascade with one another. The gate terminal of the other transistor in the complementary pair is directly applied a signal which relates to the request for interrupt on an even-numbered channel, such as the signal A0-REQ1 for the channel AO led to the block 6. The source of the first transistor Mx in said pair feeds an output BIT line, designated BIT-1 in this particular case, which is intended for reforming a given bit in the "winning" interrupt vector. Also involved in the reforming or, to use a familiar expression in the pertinent art, in the vectorizing of the interrupt signal bits for the CPU, is a group 18 of active elements including an inverter 19, a high internal resistance transistor 20, and a p-channel transistor My. The inverter has an input connected to the BIT line and an output connected to the gate of the transistor 20 and the gate of a transistor M8. This transistor M8 is in series with a transistor M9 which receives an enable signal 9 from the CPU 11 and is also designated ODD/EVEN CPU SELECTION in Figure 2, to allow a data bus allocation signal DBR of the corresponding vector The operation of the management unit of this invention will be briefly reviewed next. The inverter M1, M2 of the initial block 6 pre-charges the whole bonny chain at the start of the execution of each instruction from the microcontroller by means of the signal REQ-WA, which is re-initialized to ground GND. Following the pre-charge step, the first element 5 in the chain, that is the preceding element in the direction of propagation of the signal, can be selected if the signals on the channels REQ-WA and/or REQ-WB and/or REQ-WC have a high logic value, i.e. equal to the supply voltage Vcc. When such condition is met, the first element 5 will drive the inputs and outputs of all the other N-3 elements 5 which follow in the bonny chain to the ground value, thereby enabling the "winning" pair of interrupt channels. Thus, the first step allows that pair to be selected from the N possible interrupt pairs which is to be regarded as the winning pair. At this time, the interrupt signal vectorizing step is carried out, which means that the winning channel must be selected from the pair of winning channels and the corresponding value of the interrupt vector written into the data bus of the microcontroller. Using the value of the request signal of the pair (A0-REQ1,..., D0-REQ1), the channel to be selected is located within the winning pair. The corresponding value of the interrupt vector is then allocated to the data bus DBR through the various logic gates of the decoding portion 4. A chart is reproduced, for illustration purposes only, herein below which shows the decode logic that allocates the value of the interrupt vector to the data bus DRB. CHART: VECT 0 1 2 3 4 5 6 7 A0 0 0 0 0 A1 0 1 0 0 B0 0 0 1 0 B1 0 1 1 0 C0 0 0 0 1 C1 0 1 0 1 D0 0 0 1 1 D1 0 1 1 1 Thus, the circuit structure of this invention does solve the technical problem, and achieves a number of advantages, a main one being that the management unit 1 can be matched to various types of microcontrollers having different interrupt channels. In fact, it will be sufficient to add or remove identical elements 5 to/from the selection bonny chain, and similar modular decode cells of the interrupt vector, of the channel pairs, to have the circuit adapted to all the logics having different interrupt channel crossings.

Claims: A microcontroller interrupt management unit (1) equipped with a decoder (4) for managing a plurality (2N) of interrupt channels (2), connected to a central processing unit (11) of the microcontroller to decode and transfer thereto a single interrupt vector digital signal through said decoder (4), characterized in that it comprises a first circuit portion (3) for selecting, according to a priority, homologous pairs (A0,A1;B0,B1,...) of channels (2), incorporating a modular chain of circuit elements (5,6), each having a respective channel pair (2) connected thereto (5,6), said first portion being associated with a second decoding circuit portion (4), such that each one of a set of identical vector decoding cells in said second decoding circuit portion (4) is individually associated with a corresponding element of said modular chain comprised in said first circuit portion (3). A management unit according to Claim 1, characterized in that the interrupt vector digital signal is a re-formed interrupt vector of the channel carrying higher priority in the channel pair selected by said chain. A management unit according to Claim 1, characterized in that said chain comprises an initial block (6) effective to pre-charge the other elements (5) connected after it. A management unit according to Claim 3, characterized in that said pre-charging initial block (6) comprises a CMOS inverter (M1,M2) whereto one of said channels (2) is connected. A management unit according to Claim 1, characterized in that the number of identical modular elements (5) in the chain is equal to the number (N) of homologous channel pairs less two. A management unit according to Claim 1, characterized in that a selected chain element (5) in said modular chain of circuit elements (5,6) will drive the inputs and outputs of all the other chain circuit elements connected after it to a ground value. A management unit according to Claim 5, characterized in that each of the identical modular circuit elements (5) in the chain corresponds to the elements of a daisy chain. A management unit according to Claim 1, characterized in that each of the chain circuit elements (5,6) corresponds to one of a plurality of identical modular structures of the decoding circuit portion (4). A management unit according to Claim 8, characterized in that the circuit elements (5,6) of said chain are connected to each corresponding modular structure of the decoding portion (4) through a respective bit selection cell (7) feeding an output line (BIT). A management unit according to Claim 9, characterized in that said bit selection cells (7) are connected in cascade on the output line. A management unit according to Claim 1, characterized in that the central processing unit (11) of the microcontroller is connected to an input of the decoding circuit portion (4) to transfer a read enable signal of said interrupt vector digital signal. A microcontroller characterized in that it comprises a management unit (1) according to claim 1 or claim 3.

Inventors: BONETTI ROBERTO, BONETTI, ROBERTO
Applicants: ST MICROELECTRONICS SRL, STMICROELECTRONICS S.R.L.
Application year: 1994
Main classification: G06F13
IPC codes: G06F13